西南印度洋洋中脊热液活动区综合地质地球物理特征

Comprehensive geological and geophysical characters of hydrothermal area at Southwest Indian Ridge

西南印度洋洋中脊(SWIR)是超慢速扩张洋脊的代表,是海洋地学研究热点.本文从SWIR多波束水深数据、重、磁数据和地震结构等几方面,阐述了SWIR热液活动区(49°39′E)的综合地质地球物理特征.SWIR热液活动不仅与扩张速率有关,构造作用更是一个重要控制因素;热液活动区位于Indomed和Gallieni转换断层之间,从水深地形上看,该区段洋脊是SWIR上水深最浅的区域之一,水深与MBA存在良好的镜像关系,MBA和RMBA低值意味着较厚的地壳厚度与较高的地幔温度,洋脊段27地壳厚度大于9km,可能是受到Crozet热点的影响;磁条带数据表明,此区段洋脊南北两翼呈不对称扩张,形成南翼的浅离轴域比北翼宽;在洋脊段28发现的活动热液喷口刚好位于热液蚀变形成的低磁强区内,具有良好的硫化物资源.这些认识必将为在该区首次实施的三维地震探测研究的地质地球物理解释及活动热液喷口的动力学机制研究打下坚实基础.

outhwest Indian Ridge（SWIR） is the representative of ultraslow spreading ridges and the key area of marine geological studies.The comprehensive geological and geophysical characteristics of hydrothermal field（49°39′ E） in the SWIR were presented in this paper based on multi-beam bathymetric,gravity,magnetic data,and seismic velocity structure.The frequency of hydrothermal activities at SWIR is not simply related to spreading rate,but also tectonism playing an important role.The hydrothermal field located on the ridge segments between Indomed and Gallieni transform faults,is one of shallowest bathymetric zones where exists a close mirror image relationship between topography and mantle Bouguer anomaly（MBA）.The lows of MBA and residual mantle Bouguer anomaly（RMBA） indicate that thicker crust and higher mantle temperature in this area,and the crustal thickness in Segment #27 arrives at 9 km,which may be affected by Crozet hotspot.The banded magnetic anomalies show that the spreading is asymmetric which causing that the domain in the southern flank is wider than in the northern flank.Moreover,the first active vent discovered in Segment #28,is located at the low crustal magnetization zone which indicating good prospect of sulfide resources.The knowledge and ideas will provide a strong foundation for three-dimensional seismic survey firstly implemented in the hydrothermal area of SWIR.